316L Stainless Steel Plate Research Articles

A Study on the Fiber YAG Laser Welding of 304L Stainless Steel

This work aims to optimize the main YAG fiber laser parameters to weld 304L stainless steel plates of 3 mm thick. Different laser powers (2500, 2000, and 1500 W) and speeds (60, 40, and 20 mm/s) were used and merged in heat input, maintaining the defocusing distance at –2 mm to get full penetration. The weld quality and the effect of the laser heat input on the microstructures of the weld and heat-affected zones were investigated. Besides, the fracture strength of the welded joints and hardness distribution through the cross-sections were evaluated. The weld width has a direct relationship with heat input. The laser power of 2800 W produced full penetration joints without any macro defects while reduction in laser power pronounced partial penetration defects. The size of the heat-affected zone in all the processing parameters was very small. The microstructure of the weld zone shows columnar dendrite austenite grains with small arm spacing in most of the welded zone. The size of the dendrites became finer at lower heat input. At a higher heat input, a reasonable amount of lathy equiaxed grains with some delta ferrite occurred. A small amount of delta ferrite was detected in the heat-affected zone, which prevented the crack formation. The hardness of the weld metal was much higher than that of the base metal in all processing parameters and it has a reverse relationship with the heat input. The fracture strength of the welded joints was very close to that of the base metal in the defect-free samples and it increased with decreasing the heat input.

Proper orthogonal decomposition analysis of variable temperature field during gas tungsten arc welding

Fluid flow motion controls energy transfer in the weld pool and drives the solidification process. Experimental investigation of the fluid flow during welding is made particularly difficult by unsteady movements in the molten pool. In this paper, proper orthogonal decomposition (POD) based on images during gas tungsten arc welding (GTAW) on thin plates is used to investigate coherent structures revealed by the thermal field in the molten pool. The POD method is based on fluctuating gray levels related to surface temperature. Based on this decomposition, two dimensional spatial modes and temporal coefficients are calculated allowing the identification of regions where temperatures are correlated. To explore the potential of the POD method, weld beads were performed on a 316L stainless steel plate at three welding speeds (2.3, 3.3, and 4.3 mm s−1) and constant current (80 A). These three conditions lead to different sizes of fully penetrated weld pools and different temperature distributions. Spatial modes and temporal coefficients provide information on temperature fluctuations along the free surface. Based on POD first modes, the thermal field is reconstructed along the free surface to understand the heat transfer. Combining these results with side-view observations of the arc allows us to derive three dimensional flow patterns within the weld pool.

Evaluation of residual stresses in isothermal friction stir welded 304L stainless steel plates

Friction stir welding was performed on 304L SS plates in order to heal simulated cracks created by electrical discharge machining. Two different tool temperatures (825 and 725 °C) were chosen for this study. Both neutron diffraction and X-ray diffraction techniques were employed to evaluate the residual stresses along two orthogonal reference directions, longitudinal (σyy) and transverse (σxx). The former technique was also used to measure residual stresses at various depths. It was found that, at 1 mm depth from the top surface inside the stir zone (SZ), the longitudinal component was tensile in nature while the transverse component was compressive. The nature and magnitude of the residual stress fields, and the position of the peak residual stresses were found to vary with the weld depth. The SZ of the 725 °C weld exhibited higher peak stress than 825 °C weld mainly due to a lack of stress relief at the lower temperature.

Microstructure and microchemistry of laser welds of irradiated austenitic steels

This article investigates the integrity of laser welds on neutron irradiated, He-containing steels. Life extension of the current fleet of light water reactors could necessitate repair of cracks on irreplaceable internal components, but heat input of weld repairs exacerbates the problem by initiating He-induced cracking. Laser welding is a promising low-heat-input technology thought to limit the extent of He-induced cracking. In this study, we produce laser welds in a hot cell on AISI 304L stainless steel plates previously irradiated in the Experimental Breeder Reactor (EBR)-II. We select a systematic set of three specimens spanning fluences ~1–28 displacements per atom (dpa) at ~415–430 °C and He concentrations ~0.2–8 atomic parts per million (appm) amounting to ~0.2–2.8% swelling. He-induced cracking is observed only in specimens containing ≥3 appm He. Laser welding nearly eliminates all irradiation-induced cavities and reduces the dislocation loop number density, similar to conventional post-irradiation annealing. Microchemically, laser welding induces Cr-rich precipitation and suppresses grain boundary radiation-induced segregation. The mechanism of He-induced cracking is discussed in the context of these microchemical changes. The weld heat input is calculated and suggests that further refinement of laser welding parameters may improve the cracking resistance for higher dose and He conditions.

Electrodeposition of conductive PAMT/PPY bilayer composite coatings on 316L stainless steel plate for PEMFC application

Stainless steel fulfills most of the requirements as bipolar plates in Proton Exchange Membrane Fuel Cell. However, it undergoes severe corrosion in fuel cell operating condition. This can be resolved by coating the stainless steel with corrosion resistive conducting polymers. In this study, homogeneous and adherent conductive Poly(2-amino-5-mercapto-1,3,4- thiadiazole)/Polypyrrole (PAMT/PPY) mono and bilayer polymer composite coatings are electrosynthesized on 316L SS in 0.5 M H2SO4 by cyclic voltammetry and chronopotentiometry. The hydrophobicity and surface morphology of the coatings are analyzed by contact angle and scanning electron microscopy respectively. The polymer coatings are evaluated in 0.5 M H2SO4 medium by potentiodynamic polarization and impedance techniques at 25 °C. The polarization results reveal that PAMT on PPY composite coating shifts the Ecorr of the 316L SS towards noble direction. The EIS study reveals that the Rf value of PAMT on PPY coating is significantly higher by three orders (x103 Ωcm2) of magnitude than uncoated 316L SS. The corrosion performance of the coatings in simulated PEMFC environment is investigated by potentiodynamic and potentiostatic studies. Results show that the PAMT on PPY and PPY on PAMT bilayer coatings are stable and increased the corrosion potential by about 410–470 mV and 275–310 mV (SCE) in simulated cathodic and anodic conditions respectively. This investigation reports that the PAMT on PPY bilayer coating is serving as a good physical barrier and protecting the 316L SS against corrosion in PEMFC environment.

Mechanical properties of biomedical 316L stainless steel plates with in-plane orthogonal anisotropy by aligning crystallographical orientation via additive manufacturing

Mechanical properties of biomedical 316L stainless steel plates with in-plane orthogonal anisotropy by aligning crystallographical orientation via additive manufacturing

Processing-microstructure-property correlations for temperature-controlled friction stir welding of 304L SS plates

Friction stir welding (FSW) is being considered as a potential repair welding technique for various engineering applications. In this study, an effort was made to explore the correlation between microstructure and mechanical properties in FSWed 304L stainless steel (SS) plates. An in-house developed weld temperature control algorithm was used during FSW of 304L SS plates. FSW was performed at two different temperatures, 725 and 825 °C, in order to repair simulated cracks introduced by electrical discharge machining (EDM) in the 304L plates. Optical microscopy and scanning electron microscopy revealed ultrafine grained microstructure in some parts of the stir zone (SZ) of the FSW nugget, which is attributed to dynamic recrystallization occurring during FSW. A significant decrease in the fraction of ∑3 special boundaries with concomitant decrease in the number of annealing twins was noticed in SZ as compared to the base metal. Vickers microhardness profiles across the SZ showed increase in hardness which was due to significant grain refinement. Tensile tests were carried out across the weld bead, and failure was found to occur in the base metal, indicating an overmatching FSW nugget.

The effect of the substrate surface state on the morphology, topography and tribocorrosion behavior of Si/Zr sol-gel coated 316L stainless steel

In the present work, a Si/Zr based sol–gel (SG) coating was deposited on 316L stainless steel plates, previously treated by passivation (SSO) or electropolishing (SSEP) producing two different surface states. The SG coatings were compared for SSO and SSEP substrates in terms of morphology, topography and tribocorrosion response. The coating topography revealed a smoother surface for the Si/Zr-SSEP system. The coating deposited on the smoothest surface (Si/Zr-SSEP) presented half of the thickness of the one deposited on the roughest surface (Si/Zr-SSO). Tribocorrosion behavior was studied under potentiostatic control at anodic potential with a continuous recording of current (I) during sliding (pin-on-disc and alumina ball counterbody). Both SG systems showed an increase of current upon 100 sliding contact cycles indicating corrosion activity. After tribocorrosion tests, both systems revealed scratches, typical of abrasion, and coating removal in the wear tracks; the alumina counterparts presented accumulation of wear particles adhered to their surfaces. In conclusion, the initial surface state of the substrate modified the coating thickness, topography but did not significantly alter the tribocorrosion response of the studied SG systems.

The behavior of TIG welding arc in a high-frequency axial magnetic field

The effect of high-frequency axial magnetic field (HFAMF) on the shape of the welding arc and welding formation of tungsten inert gas (TIG) welding is analyzed theoretically and experimentally. The 316L stainless steel plate was welded with HFAMF produced by the excitation coil installed on the welding torch. The influence of the HFAMF on the welding process is studied by changing the magnetic frequency from 0 to 2000 Hz. The experimental results show that when the magnetic field frequency reaches 1500 Hz, the arc rotation radius is decreased to the minimum; the arc shape changes from cone to compressed cylinder; and the arc temperature, the arc pressure, and the depth-width ratio of the weld beam reached the maximum. Otherwise, the effect of applied HFAMF on the stress of arc and weld pool is discussed, and the mechanism of arc contraction is analyzed.

Synthesis and characterization of hexamethyldisilane films deposited on stainless steel by plasma-enhanced chemical vapour deposition

Films deposited on 316L stainless steel plates by plasma-enhanced chemical vapour deposition (PECVD) using hexamethyldisilane (HMDS) in the liquid phase as precursor were studied. We have determined their structural, mechanical, and tribological properties. The samples were deposited at 300 °C with a different self-bias voltage ranging from −150 V to −450 V. The films were characterized by X-Ray photoelectron spectroscopy and infrared absorption spectroscopy to determine the atomic concentrations and identify the chemical environment of the atoms in the films. Raman spectroscopy revealed the presence of carbons with sp2 hybridization. The films have a polymeric character, as suggested by the strong luminescence background present in Raman spectra. Nanoindentation technique was used to measure the hardness of the film. Tribological properties were determined by reciprocal linear disc tests. Our results show that the carbon films prepared by PECVD using HMDS as precursors have high hardness and low friction coefficient.

Structural condition monitoring and identification of laser cladding metallic panels based on an acoustic emission signal feature optimization algorithm

Laser cladding technology has become a central issue in industrial research and application recently. Due to the complexity of the processing and the difficulty of quantitative analysis, it is particularly important to effectively and reliably detect the forming quality of the cladding layer. Therefore, the laser cladding processing condition of metallic panels is monitored and identified based on acoustic emission technology in this article. Consequently, laser cladding acoustic emission signal of 316L stainless steel plate is first collected, and a multi-domain acoustic emission signal feature extraction method based on time–frequency domain and waveform parameters is constructed by integrating time–frequency, empirical, and inter-relationship diagraph analysis. Moreover, a feature optimization approach based on t-distributed stochastic neighbor embedding algorithm is proposed, which combines with correlation analysis to realize the de-redundancy and optimization of acoustic emission signal features. In addition, on the basis of optimizing the characteristics of acoustic emission signal, laser cladding acoustic emission signals under three technological parameters are collected. Second, a laser cladding condition identification method, which is a least square support vector machine algorithm based on niche particle swarm optimization, is proposed. The optimal parameter combination of niche particle swarm optimization algorithm is mainly selected to improve the accuracy of identification and classification. The results demonstrate the proposed t-distributed stochastic neighbor embedding feature optimization method can effectively extract the sensitive information related to the processing condition in the feature space, and the optimization of least square support vector machine parameters through niche particle swarm optimization can significantly improve the identification rate of classification. Specifically, the feasibility of the proposed t-distributed stochastic neighbor embedding–niche particle swarm optimization–least square support vector machine model to analyze laser cladding acoustic emission signal characteristics is verified, and the effectiveness of acoustic emission–based structural condition monitoring and identification of laser cladding plate-like structures is also demonstrated.

Effect of particle concentration on the tribological properties of NBR sealing pairs under contaminated water lubrication conditions

The abrasive wear behavior of elastomers has attracted a lot of attention and interest in order to better comprehend its effect on the service performance of the fluid sealing pairs. The objective of this work was to study the tribological performance of the fluid sealing pairs under various abrasive concentration conditions. Therefore, this study developed an abrasive wear test experiment for an acrylonitrile–butadiene rubber (NBR) cylinder against 316L stainless steel plate tribo-pairs to evaluate reciprocating sliding tests under different particle concentrations.Results demonstrate that the abrasives feature strong aggressivity, which impedes the formation of a good friction-reduction water film, results in weak lubrication, changes the friction coefficient and wear rate, and deteriorates the tribological performance of the tribo-pairs. The friction coefficients of the low abrasive concentration are relatively small, and the friction coefficient increases with increasing abrasive concentration.At different abrasive concentrations and sizes, the rubber matrix is attacked in various forms by the hard particles, which appear as pinning, particle agglomeration embedment, and abrasive flow erosion. Particle concentration affects the damage behavior of the tribo-pairs, and the particles easily enter the interface of the tribo-pairs when their concentration is high.

Evaluation of through-thickness residual stresses in conventional and narrow grooved stainless steel welds

Thick AISI 304L stainless steel plates were welded using the gas metal arc welding process, and through-thickness residual stresses were evaluated by finite element simulation and the deep hole drilling technique. 3D moving heat source-based thermo-mechanical models were implemented to evaluate through-thickness residual stresses. The effects of the weld groove geometries and external restraints on the pattern of through-thickness residual stresses were studied. The maximum magnitude of locked-in residual stresses was recorded beneath the top surface, at a depth of around 6 mm. In comparison to conventional weld groove, the narrow weld groove configuration exhibited a 20–40% reduction in peak residual stresses. A significant rise in residual stresses was observed in constrained welds. The effect of the yield strength of the filler material on the evaluation of the through-thickness residual stress distribution in the course of finite element modeling was illustrated. The evolution of through-thickness residual stresses was also assessed concerning each weld pass.

Microstructure and mechanical properties of dissimilar Ti/Nb/Cu/steel laser joints

The absence of intermetallic phases in Fe/Cu, Cu/Nb and Nb/Ti binary systems opens the possibility to obtain reliable joints between titanium alloys and steels by using a multimaterial copper/niobium insert. Continuous Yb:YAG laser welding of 1 mm thick titanium and 316L stainless steel plates through niobium/copper multimaterial insert was performed. The use of a 100 µm laser beam allowed producing isolated molten zones and thus completely avoiding the formation of brittle intermetallic phases, according to SEM and XRD analysis. The effect of energy per unit length applied to the niobium/copper welds on the mixing process and mechanical properties of the joints was investigated. A ductile fracture systematically occurred in the unmelted copper zone of the joints at maximal average UTS of 250 MPa.

Effects of heat treatment on fracture mechanism of martensite/austenite MLS composite plates by hot roll bonding

The martensite/austenite MLS composite plates were fabricated by hot roll bonding of the alternately stacked 2Cr13 and 316L stainless steel plates. The effects of heat treatment on the microstructure transformation, interface behavior, tensile properties, fracture modes and failure mechanisms have been studied in depth. The microstructure of the composite plates is composed of austenite in 316L layers, martensite and a small amount of ferrite in 2Cr13 layers. After heat treatment, the microstructure of the composite plates changes from rolling texture to equiaxed grains. Most importantly, the recrystallization and thermal diffusion formed after heat treatment can effectively increase the overall plasticity of composite plates at the expense of small strength and hardness, improve the interface deformation compatibility and interfacial bonding strength, change the fracture mode from the quasi-cleavage fracture into the full dimple fracture, and fracture mechanism from the interface failure into the intralayer failure.

Thermal performance of a novel flat thermosyphon for avionics thermal management

In this study, a novel flat thermosyphon was conceived to operate as a thermally active chassis wall of avionics enclosures. The flat thermosyphon, specifically designed to operate in vertical orientation, has the dimensions: 320 × 193 × 24 mm and consists of nine 316L stainless steel plates stacked and diffusion bonded. The flat thermosyphon was fabricated and tested under five different heating conditions, allowing for the study of the influence of the heater size and position on its thermal performance. Heat was added to the evaporator by aluminum heater blocks (50 × 50 mm) within which internal cartridge resistances are lodged, and it was extracted from the condenser by natural convection. Four filling ratios were tested (7.5%, 15%, 30% and 50%). The empty thermosyphon, in which only conduction heat transfer takes place, was also tested for comparison purposes. The input power varied from 15 W to 60 W. In total, the novel device was tested under fifteen different configurations. Test results are presented in terms of the temperature evolution with time, the thermal resistance (one-dimensional and spreading) and the temperature uniformity on the condenser surface. The filling ratio severely influenced the thermal performance of the device. The thermal resistance varied from 0.047 to 0.327 °C/W for tests with the optimum filling ratio of 7.5%. The increase in input power improved the thermal performance of the flat thermosyphon, whereas the decrease in heater size negatively affected it. The thermal resistance results showed that the spreading is the dominant and that this dominance increases with the decrease in heater size. In addition, the thermal resistance of the novel flat thermosyphon was proved competitive when compared to other flat heat pipes studied in the literature.

Assessment of characteristics and cytotoxic effects of 316L stainless steel coated with a new titanium oxide nano-structure coating method

In order to fabricate the TiO2 nano-structure coating on the Ti-free stainless steel with good adhesion, commercially obtained 316L stainless steel (316L SS) plates were chemically treated by KOH aqueous solution including TiH2 powder at 60ºC for 3 days in an oil bath shaker, and subsequently heated up to 550-800ºC under the air atmosphere. The crystal structure, color, adhesive strength and cytotoxic effects of coating were investigated. Fiber-like hydrogen titanate nano-structures were formed on the 316L SS surface and made a fine network. X-ray diffraction (XRD) patterns showed that hydrogen titanate phase converted to anatase and rutile after heat treatment above 550ºC. The heat treated sample at 800ºC for 1 h showed the highest adhesive strength and the lowest cytotoxicity. The alkali treatment method in this study is expected to be used on the other Ti-free metals with further research.

Numerical and experimental investigation on laser metal deposition as repair technology for 316L stainless steel

316L stainless steel plate with a trapezoidal groove was repaired by laser metal deposition (LMD) with 316L stainless steel powder. Finite element method (FEM) is adopted to predict the thermal behavior in the molten pool during the LMD. There is an overlapping between the adjacent tracks and adjacent layers during the LMD, forming a three dimensional structure. The influence of the second track in the first layer and the first track in the second layer on the first track in the first layer was investigated by the simulation process and experimental method. The numerical results indicated that the maximum temperature and the dimensions of the molten pool at the second track in the first layer and the first track in the second layer are larger than those at the first track in the first layer. The temperature of the first track in the first layer increases after the deposition of the second track in the first layer and the first track in the second layer. The microstructure evolution of the first track in the first layer was examined by the optical microscope (OM) and scanning electron microscope (SEM). The experimental results show that the thermal cycle caused by adjacent tracks brings about a significant effect on the microstructure and micro-hardness of the first track in the first layer.

Effects of toolpath and clamping strategies in machining distortion of stainless-steel parts

Heat exchangers in new nuclear power generation plants are made of thin AISI 316L stainless-steel plates stacked together in order to improve their efficiency and compactness. To ensure the assembly, the global distortion of those plates must be mastered and minimized, mainly by predicting the evolution of the residual stress field during their manufacturing process chain. During machining, those residual stresses are redistributed to reach another equilibrium state, leading to a macroscopic part distortion. The main objective of this work is to study experimentally the influence of the machining toolpath and clamping strategies on the global part distortion. Then, a part distortion model is developed in order to verify the clamping effect on the distortion.

Towards attaining dissimilar lap joint of CuCrZr alloy and 316L stainless steel using friction stir welding

ABSTRACTCuCrZr alloy (Cu-0.8wt-%Cr-0.1wt-%Zr) and 316L stainless steel (Fe-0.03wt-%C-16wt-%Cr-10wt-%Ni) plates were successfully friction stir lap welded resulting in significant mechanical mixing of the two matrix elements, Cu and Fe, in the stir zone. The severe mixing not only led to improved load bearing response but also leads to form Cu-rich and Fe-rich regions in the weld nugget. The formation of these phases governs the failure mechanism of the joint. Tensile properties of the weld showed promising response when compared with joints made for the similar alloy pair by other welding techniques. This suggests strong feasibility of applying FSW for joining Cu and steel for nuclear applications.